As shown by Heath et al., U.S. Pat. No. 3,847,867, polyetherimides were made by the melt polymerization of aromatic bis(ether anhydride) and organic diamine to provide for the production of injection moldable high performance thermoplastics. It has been found, for example, that when aromatic bis(ether anhydride) such as 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride referred to hereinafter as "BPADA" is melt polymerized with meta-phenylene diamine, polyetherimide is obtained having a Tg in the range of from about 219.6.degree. to 229.1.degree. C. Improved results have been achieved by utilizing other aromatic diamines in place of meta-phenylene diamine such as sulfone bis(phenylamine) to improve the Tg and heat distortion temperature of the resulting polyetherimide to satisfy particular applications.
The present invention is based on my discovery that certain bis(dialkyl aromatic ether anhydride) having the formula ##STR1## where R, R.sup.1, R.sup.2 and R.sup.3 are C.sub.(1-4) alkyl radicals, hereinafter referred to as "TMBPADA", has been found to provide polyetherimide having a substantially enhanced Tg and heat distortion temperature when melt polymerized with metaphenylene diamine as compared to polyetherimide made by the same procedure from BPADA. Further improvements in Tg and heat distortion temperature can be achieved by melt polymerizing TMPADA with aromatic diamines such as sulfone bis(phenyl amine) referred to hereinafter as "p.sup.2 SDAN" to form polyetherimide having Tg's as high as 292.7.degree. C. Surprisingly, although the heat distortion temperature of the resulting polyetherimides are substantially enhanced as the result of using TMBPADA, in accordance with the practice of the present invention, the processability of the resulting polyetherimide is not adversely affected.